Coating Process

Coating is carried out by a process known as Physical Vapour Deposition (PVD). The coating material is heated and evaporated in a vacuum, this then condenses on the substrate which is mounted at the top of the chamber.

Evaporation in the facility is carried out by two methods:

a) Thermal evaporation. The material is placed in a conducting boat which is connected between two terminals. High current is passed through the boat until it glows, this then causes the material to heat up and evaporate.

b) Electron Beam Evaporation (ebeam) In this method the material is placed in a crucible which is then placed in a hearth. The material is bombarded by a beam of electrons which heats and vaporises it. The electrons are emitted by a glowing filament and attracted to the hearth by a potential difference. The beam is directed and focused on the material in the crucible by a magnetic field. Supplementary magnetic fields allow positioning of the focused spot in order to maintain a constant rate of evaporation.

Layer thickness monitoring is essential for thin film work. Even small percentage errors can cause unwanted and detrimental effects in the final product. The thickness of the growing layer can be monitored by an oscillating quartz crystal arrangement which is exposed to the evaporant in the the chamber. As the crystal becomes coated the oscillation frequency of the crystal falls and this is translated into a thickness value by the controller.